2-cyanoacrylate adhesive composition

ABSTRACT

An adhesive composition is provided which is excellent in adhesion rate on non-polar hard-to-bond materials and bond gap curability, and further is good in storage stability. It is a 2-cyanoacrylate-based adhesive composition which includes (a) a 2-cyanoacrylic acid ester and (b) an onium salt represented by the following general formula (1): 
         n C + A −   n -X  (1)
 
     wherein, in formula (1), C +  represents an onium cation, A −  represents at least one anion selected from the group consisting of —SO 3   − , —OSO 3   −  and a specific imide anion, X represents a linking group which connects at least two anions together, and n is an integer of 2 or more.

TECHNICAL FIELD

The present invention relates to a 2-cyanoacrylate-based adhesivecomposition containing a 2-cyanoacrylic acid ester as the principalcomponent.

BACKGROUND ART

A 2-cyanoacrylate-based adhesive composition quickly establishes astrong bonding among various types of materials based on the uniqueanion polymerization characteristics exhibited by its principalcomponent, 2-cyanoacrylic acid ester, which initiates polymerizationunder the presence of weak anion provided by slight moisture or the likeattached to a surface of an adherend. Accordingly, it is used as theso-called instantaneous adhesive in a wide range of fields includingindustrial, medical, and household applications. However, since thesetting of the 2-cyanoacrylate-based adhesive composition proceeds byanion polymerization, problems of lowered adhesion rate and insufficientadhesion strength resulting from inhibition of anion polymerization havebeen found when adherends are made of wood which is acidic or a metalwhich easily forms an oxide skin. Furthermore, problems of anionpolymerization suppression and lowered adhesion rate have been foundwhen adherends are hard-to-bond materials because of low polarity likenatural rubbers. Furthermore, such a problem that it takes really longtime to cure at a site where a gap exists between adherends to be bondedtogether (hereinafter referred to as “bond gap curability”) has beenfound.

To overcome such problems, various types of additives have been proposedheretofore. For instance, Patent Document 1 discloses an adhesivecomposition containing crown ethers, and Patent Document 2 discloses anadhesive composition containing polyalkylene oxides. Further, PatentDocuments 3 and 4 disclose adhesive compositions containing calixarenes.Patent Document 5 describes using a phase transfer catalyst as ahardening accelerator for the 2-cyanoacrylate-based composition.Furthermore, Patent Document 6 describes a 2-cyanoacrylate-basedcomposition containing a trihalogenated alkanesulfonate as a compositionthat is excellent in storage stability and is hardened quickly.

CONVENTIONAL TECHNICAL DOCUMENTS Patent Documents

Patent Document 1: Japanese Patent Publication (Laid-open) No. Sho.53-129231

Patent Document 2: Japanese Patent Publication (Laid-open) No. Sho.63-128088

Patent Document 3: Japanese Patent Publication (Laid-open) No. Sho.60-179482

Patent Document 4: Japanese Patent Publication (Laid-open) No.2000-44891

Patent Document 5: British Patent Publication GB2228943 specification

Patent Document 6: Japanese Patent Publication (Laid-open) No.2000-73014

SUMMARY OF INVENTION Problems to be Solved by the Invention

The adhesive compositions disclosed in Patent Documents 1 to 5 haveaccelerated adhesion rate for various adherends, however, withincreasing demand on productivity, the adhesion rate on non-polarhard-to-bond materials and bond gap curability are still notsatisfactory. The adhesive composition disclosed in Patent Document 6 iseffective to have storage stability improved, but is still insufficientin bond gap curability.

The present invention is made in light of the aforementionedcircumstances, and aims at providing an adhesive composition which issuperior in adhesion rate for non-polar hard-to-bond materials and bondgap curability and further excellent in storage stability.

Means for Solving the Problems

The present inventors have found that an adhesive composition which isimproved adhesion rate for non-polar hard-to-bond materials and bond gapcurability and further superior in storage stability can be obtained byblending an onium salt having a specific polyfunctional structure with a2-cyanoacrylic acid ester, and have accomplished the present invention.

The present invention is as follows:

1. A 2-cyanoacrylate-based adhesive composition which comprises (a) a2-cyanoacrylic acid ester and (b) an onium salt represented by thefollowing general formula (1):

nC⁺A⁻ _(n)-X  (1)

wherein, in formula (1), C⁺ represents an onium cation, A⁻ represents atleast one anion selected from the group consisting of —SO₃ ⁻, —OSO₃ ⁻and an imide anion represented by the following formula (2), Xrepresents a linking group which connects at least two anions together,and n is an integer of 2 or more.

wherein, in formula (2), R¹ represents a fluorine atom, alkyl group,cycloalkyl group, perfluoroalkyl group, aryl group, aralkyl group,alkenyl group or alkynyl group.

2. The 2-cyanoacrylate-based adhesive composition according to the aboveitem 1, wherein the cation of the onium salt (b) is at least one oniumcation selected from a group consisting of a quaternary ammonium cation,a quaternary phosphonium cation, an imidazolium cation, a pyridiniumcation, and a tertiary sulfonium cation.

3. The 2-cyanoacrylate-based adhesive composition according to the aboveitem 1 or 2, wherein the anion of the onium salt (b) is at least oneanion selected from a group consisting of —SO₃ ⁻, —OSO₃ ⁻, afluorosulfonylimide anion and a perfluoroalkylsulfonylimide anion.

4. The 2-cyanoacrylate-based adhesive composition according to any oneof the above items 1 to 3, wherein the linking group X in the abovegeneral formula (1) is a divalent linking group.

5. The 2-cyanoacrylate-based adhesive composition according to the aboveitem 4, wherein the linking group X in the above general formula (1) isat least one divalent linking group selected from the group consistingof an alkylene group, a cycloalkylene group, an arylene group and abiphenyl group.

6. The 2-cyanoacrylate-based adhesive composition according to any oneof the above items 1 to 5, wherein the content of the onium salt (b) is10 to 20,000 ppm relative to 100 parts by mass of the 2-cyanoacrylicacid ester (a).

Effect of the Invention

The 2-cyanoacrylate-based adhesive composition according to the presentinvention contains a 2-cyanoacrylic acid ester and an onium salt with apolyfunctional structure linked via the linking group X, and thus isimproved in adhesion rate for non-polar hard-to-bond materials and bondgap curability, and is also excellent in storage stability.

DESCRIPTION OF EMBODIMENTS

Details of the 2-cyanoacrylate-based adhesive composition (which ishereinafter often simply referred to as “adhesive composition”)according to the present invention are described below.

The adhesive composition of the present invention contains (a) a2-cyanoacrylic acid ester and (b) an onium salt having a specificstructure.

As the “(a) 2-cyanoacrylic acid ester”, 2-cyanoacrylic acid estersgenerally employed in this type of adhesive compositions can be usedwithout any particular restriction. The 2-cyanoacrylic acid esterincludes methyl, ethyl, chloroethyl, n-propyl, i-propyl, allyl,propargyl, n-butyl, i-butyl, n-pentyl, n-hexyl, cyclohexyl, phenyl,tetrahydrofurfuryl, heptyl, 2-ethylhexyl, n-octyl, 2-octyl, n-nonyl,oxononyl, n-decyl, n-dodecyl, methoxyethyl, methoxypropyl,methoxyisopropyl, methoxybutyl, ethoxyethyl, ethoxypropyl,ethoxyisopropyl, propoxymethyl, propoxyethyl, isopropoxyethyl,propoxypropyl, butoxymethyl, butoxyethyl, butoxypropyl, butoxyisopropyl,butoxybutyl, 2,2,2-trifluoroethyl, and hexafluoroisopropyl esters of2-cyanoacrylic acid. These 2-cyanoacrylic acid esters can be used aloneor in combination of two or more. Furthermore, among these2-cyanoacrylic acid esters, 2-cyanoacrylic acid esters having an alkylgroup with 3 or less carbon atoms are preferred since they are excellentin curability, and ethyl 2-cyanoacrylate is more preferred.

The adhesive composition according to the present invention contains“(b) an onium salt represented by the following general formula (1)”.The onium salt is a compound that functions as a hardening acceleratorof the adhesive composition and particularly improves adhesion rate fornon-polar hard-to-bond materials and bond gap curability.

nC⁺A⁻ _(n)-X  (1)

wherein, in formula (1), C⁺ represents an onium cation, A⁻ represents atleast one anion selected from the group consisting of —SO₃ ⁻, —OSO₃ ⁻and an imide anion represented by the following formula (2), Xrepresents a linking group which connects at least two anions together,and n is an integer of 2 or more,

wherein, in formula (2), R¹ represents a fluorine atom, alkyl group,cycloalkyl group, perfluoroalkyl group, aryl group, aralkyl group,alkenyl group or alkynyl group.

The cations of the onium salt are not particularly limited as long asthey can impart solubility in 2-cyanoacryalte to the onium salt, andinclude, for example, an onium cation represented by the followinggeneral formula (3), an imidazolium cation, a pyridinium cation, and anonium cation represented by the following general formula (4).

wherein, in formula (3), R² to R⁵ each independently represents anon-substituted or substituted alkyl group, cycloalkyl group, arylgroup, aralkyl group, alkenyl group or alkynyl group; otherwise, part orall of R² to R⁵ may form a non-substituted or substituted 3 to 10membered ring together with the atom represented by Z wherein the ringmay contain a hetero atom such as O and S, provided that R² to R⁵ whichdo not involve the formation of the ring are the same as definedhereinbefore; and Z represents a nitrogen atom or phosphorus atom.Specific examples of the above substituted alkyl group include, forexample, an alkoxy group and an alkanoyl group. The abovenon-substituted or substituted alkyl group preferably has 1 to 20 carbonatoms, and more preferably 1 to 16 carbon atoms. When part of R² to R⁵form a ring, the ring is, in general, constituted by 2 to 3 of R² to R⁵.Specific examples of the compound represented by the formula (3) inwhich two of R² to R⁵ form a ring include piperidinium cation,morpholinium cation, and pyrrolidinium cation.

wherein, in formula (4), R⁶ to R⁸ each independently represents anon-substituted or substituted alkyl group, cycloalkyl group, arylgroup, aralkyl group, alkenyl group or alkynyl group; otherwise, part orall of R⁶ to R⁸ may form a non-substituted or substituted 3 to 10membered ring together with the sulfur atom wherein the ring may containa hetero atom such as O and S, provided that R⁶ to R⁸ which do notinvolve the formation of the ring are the same as defined hereinbefore.Specific examples of the above substituted alkyl group include, forexample, an alkoxy group and an alkanoyl group. The abovenon-substituted or substituted alkyl group preferably has 1 to 20 carbonatoms, and more preferably 1 to 16 carbon atoms.

Representative examples of the onium cations represented by the formula(3) include quaternary ammonium cations, quaternary phosphonium cations,and the like.

Specific examples of the quaternary ammonium cations includetetraalkylammonium cations such as tetramethylammonium,ethyltrimethylammonium, diethyldimethylammonium, triethylmethylammonium,tetraethylammonium, tetra-n-butylammonium, trimethyl-n-propylammonium,trimethyl-isopropylammonium, n-butyltrimethylammonium,isobutyltrimethylammonium, t-butyltrimethylammonium,n-hexyltrimethylammonium, dimethyldi-n-propylammonium,dimethyldiisopropylammonium, dimethyl-n-propylisopropylammonium,methyltri-n-propylammonium, methyltri-isopropylammonium,methyldi-n-propylisopropylammonium, methyl-n-propyldiisopropylammonium,triethyl-n-propylammonium, triethylisopropylammonium,n-butyltriethylammonium, triethylisobutylammonium,t-butyltriethylammonium, di-n-butyldimethylammonium,diisobutyldimethylammonium, di-t-butyldimethylammonium,n-butylethyldimethylammonium, isobutylethyldimethylammonium,t-butylethyldimethylammonium, n-butylisobutyldimethylammonium,n-butyl-t-butyldimethylammonium, t-butylisobutyldimethylammonium,diethyldi-n-propylammonium, diethyldiisopropylammonium,diethyl-n-propylisopropylammonium, ethyltri-n-propylammonium,ethyltriisopropylammonium, ethylisopropyldi-n-propylammonium,ethyldiisopropyl-n-propylammonium, diethylmethyl-n-propylammonium,ethyldimethyl-n-propylammonium, ethylmethyldi-n-propylammonium,diethylisopropylmethylammonium, ethylisopropyldimethylammonium,ethyldiisopropylmethylammonium, ethylmethyl-n-propylisopropylammonium,tetra-n-propylammonium, tetra-isopropylammonium,tri-isopropyl-n-propylammonium, diisopropyldi-n-propylammonium,isopropyl-tri-n-propylammonium, butyltrimethylammonium,trimethylpentylammonium, hexyltrimethylammonium,heptyltrimethylammonium, trimethyloctylammonium, trimethylnonylammonium,decyltrimethylammonium, trimethylundecylammonium,dodecyltrimethylammonium, didecyldimethylammonium,dilauryldimethylammonium, dimethyldistyrylammonium,dimethyldioctadecylammonium, dimethyldioctylammonium,dimethyldipalmitylammonium, ethylhexadecyldimethylammonium,hexyldimethyloctylammonium, dodecyl(ferrocenylmethyl)dimethylammonium,N-methyl homatropinium and the like; aromatic alkyl-group substitutedammonium cations such as benzyltrimethylammonium,benzyltributylammonium, benzyldodecyldimethylammonium, and the like;aromatic substituted ammonium cations such as trimethylphenylammonium,tetraphenylammonium, and the like; and aliphatic cyclic ammonium cationssuch as pyrrolydinium (such as 1,1-dimethylpyrrolydinium,1-ethyl-1-methylpyrrolydinium, 1,1-diethylpyrrolydinium,1,1-tetramethylenepyrrolydinium, and 1-butyl-1-methylpyrrolydinium),piperidinium (such as 1,1-dimethylpiperidinium, 1-ethyl-1-methylpiperidinium, 1,1-diethylpiperidinium, and1-butyl-1-methylpiperidinium), and morpholinium (such as1,1-dimethylmorpholinium, 1-ethyl-1-methylmorpholinium, and1,1-diethylmorpholinium).

Specific examples of the quaternary phosphonium cations include cationssuch as tetramethylphosphonium, triethylmethylphosphonium, andtetraethylphosphonium.

Specific examples of the imidazolium cations include cations such as1,3-dimethylimidazolium, 1,2,3-trimethylimidazolium,1-ethyl-3-methylimidazolium, 1-ethyl-2,3-dimethylimidazolium,1-methyl-3-n-octylimidazolium, 1-hexyl-3-methylimidazolium,1,3-diethylimidazolium, 1,2-diethyl-3-methylimidazolium,1,3-diethyl-2-methylimidazolium, 1,2-dimethyl-3-n-propylimidazolium,1-n-butyl-3-methylimidazolium, 1-n-butyl-2,3-dimethylimidazolium,1,2,4-trimethyl-3-n-propylimidazolium, 1,2,3,4-tetramethylimidazolium,1,2,3,4,5-pentamethylimidazolium, 2-ethyl-1,3-dimethylimidazolium,1,3-dimethyl-2-n-propylimidazolium, 1,3-dimethyl-2-n-pentylimidazolium,2-n-heptyl-1,3-dimethylimidazolium, 1,3,4-trimethylimidazolium,2-ethyl-1,3,4-trimethylimidazolium, 1,3-dimethylbenzimidazolium,3-methyl-1-phenylimidazolium, 1-benzyl-3-methylimidazolium,2,3-dimethyl-1-phenylimidazolium, 1-benzyl-2,3-dimethylimidazolium,1,3-dimethyl-2-phenylimidazolium, 2-benzyl-1,3-dimethylimidazolium,1,3-dimethyl-2-n-undecylimidazolium, and1,3-dimethyl-2-n-heptadecylimidazolium.

The pyridinium cations include cations such as 1-methylpyridinium,1-ethylpyridinium, 1-n-propylpyridinium, 1-isopropylpyridinium,1-n-butylpyridinium, and 1-n-butyl-3-methylpyridinium.

Specific examples of the tertiary sulfonium cations represented by thegeneral formula (4) above include cations such as trimethylsulfonium,triethylsulfonium, tripropylsulfonium, and triphenylsulfonium.

Among the aforementioned onium cations, preferred are quaternaryammonium cations, the quaternary phosphonium cations, imidazoliumcations, pyridinium cations, or tertiary sulfonium cations from theviewpoint of exhibiting excellent solubility to 2-cyanoacrylic acidester and good balance between high curing acceleration property andstorage stability of the adhesive composition; and further preferred arequaternary ammonium cations, imidazolium cations or pyridinium cations.

Next, the anion of the onium salt has a structure in which at least oneanion selected from the group consisting of —SO₃ ⁻, —OSO₃ ⁻ and an imideanion represented by the following formula (2) is linked via the linkinggroup X. When the anion is another anion than the above described ones,for example, phosphonate anion and alkylphosphate, the onium saltbecomes basic and thus causes polymerization of 2-cyanoacrylic acidesters during storage, thereby leading to degradation of storagestability.

wherein, in formula (2), R¹ represents a fluorine atom, alkyl group,cycloalkyl group, perfluoroalkyl group, aryl group, aralkyl group,alkenyl group or alkynyl group.

Among the above described anions, preferred are —SO₃ ⁻, —OSO₃ ⁻, afluorosulfonylimide anion and a perfluoroalkylsulfonylimide anion fromthe viewpoint of adhesion rate for non-polar hard-to-bond materials,bond gap curability and storage stability of the adhesive composition,and more preferred are —SO₃ ⁻ and —OSO₃ ⁻.

The linking group X which connects the above described anions togetheris preferably a divalent to tetravalent lining group from the viewpointof solubility of the onium salt in 2-cyanoacrylic acid esters, morepreferably a divalent linking group. Also, the linking group X is notparticular limited as long as it can provide solubility to2-cyanoacrylic acid esters. The linking group is preferably an organicgroup. Specific examples thereof include a structure selected from thegroup consisting of a hydrocarbon group which may have a substituent, anaromatic ring, a double bond, a triple bond, a cyclic structure, anester bond, an ether bond, a thioether bond, a siloxane bond and acombination of these, and particularly preferable is an alkylene group,a cycloalkylene group, an arylene group or a biphenyl group. The abovesubstituent includes an alkanoyl group, a halogen atom, a silyl group, anitro group, an azide group, a cyano group, a nitroso group and thelike.

In the above general formula (1), n is determined by the valency of thelinking group X, and n is preferably an integer of 2-4, and morepreferably n=2.

The onium salt used in the present invention is not particularly limitedso long as it is a combination of the cations and the anions describedhereinbefore. Specific examples of the onium salt having a divalentlinking group include bis(tetraethylammonium) 1,2-ethanedisulfonate,bis(tetra-n-butylammonium) 1,2-ethanedisulfonate,bis(methyltri-n-octylammonium) 1,2-ethanedisulfonate,bis(amyltriethylammonium) 1,2-ethanedisulfonate,bis(cyclohexyltrimethylammonium) 1,2-ethanedisulfonate,bis(1-ethyl-3-methylimidazolium) 1,2-ethanedisulfonate,bis(1-ethyl-2,3-dimethylimidazolium) 1,2-ethanedisulfonate,bis(1-butyl-3-methylimidazolium) 1,2-ethanedisulfonate,bis(1-butyl-2,3-dimethylimidazolium) 1,2-ethanedisulfonate,bis(1-methyl-3-n-octylimidazolium) 1,2-ethanedisulfonate,bis(1-hexyl-3-methylimidazolium) 1,2-ethanedisulfonate,bis(2-ethyl-1,3-dimethylimidazolium) 1,2-ethanedisulfonate,bis(1,3-dimethyl-2-n-propylimidazolium) 1,2-ethanedisulfonate,bis(1,3-dimethyl-2-n-pentylimidazolium) 1,2-ethanedisulfonate,bis(2-n-heptyl-1,3-dimethylimidazolium) 1,2-ethanedisulfonate,bis(1-ethyl-1-methylpiperidinium) 1,2-ethanedisulfonate,bis(1-butyl-1-methylpiperidinium) 1,2-ethanedisulfonate,bis(1-ethyl-1-methylpyrrolidinium) 1,2-ethanedisulfonate,bis(1-butyl-1-methylpyrrolidinium) 1,2-ethanedisulfonate,bis(1-methyl-1-propylpyrrolidinium) 1,2-ethanedisulfonate,bis(1-ethylpyridinium) 1,2-ethanedisulfonate,bis(1-ethyl-3-methylpyridinium) 1,2-ethanedisulfonate,bis(1-butyl-3-methylpyridinium) 1,2-ethanedisulfonate,bis(1-ethyl-4-methylpyridinium) 1,2-ethanedisulfonate,bis(1-butylpyridinium) 1,2-ethanedisulfonate,bis(1-butyl-4-methylpyridinium) 1,2-ethanedisulfonate,bis(tetramethylphosphonium) 1,2-ethanedisulfonate,bis(triethylmethylphosphonium) 1,2-ethanedisulfonate,bis(tetraethylphosphonium) 1,2-ethanedisulfonate, and the like.

Further, other specific examples of the onium salt having a divalentlinking group include bis(tetraethylammonium) 1,4-butanedisulfonate,bis(tetra-n-butylammonium) 1,4-butanedisulfonate,bis(methyltri-n-octylammonium) 1,4-butanedisulfonate,bis(amyltriethylammonium) 1,4-butanedisulfonate,bis(cyclohexyltrimethylammonium) 1,4-butanedisulfonate,bis(1-ethyl-3-methylimidazolium) 1,4-butanedisulfonate,bis(1-ethyl-2,3-dimethylimidazolium) 1,4-butanedisulfonate,bis(1-butyl-3-methylimidazolium) 1,4-butanedisulfonate,bis(1-butyl-2,3-dimethylimidazolium) 1,4-butanedisulfonate,bis(1-methyl-3-n-octylimidazolium) 1,4-butanedisulfonate,bis(1-hexyl-3-methylimidazolium) 1,4-butanedisulfonate,bis(2-ethyl-1,3-dimethylimidazolium) 1,4-butanedisulfonate,bis(1,3-dimethyl-2-n-propylimidazolium) 1,4-butanedisulfonate,bis(1,3-dimethyl-2-n-pentylimidazolium) 1,4-butanedisulfonate,bis(2-n-heptyl-1,3-dimethylimidazolium) 1,4-butanedisulfonate,bis(1-ethyl-1-methylpiperidinium) 1,4-butanedisulfonate,bis(1-butyl-1-methylpiperidinium) 1,4-butanedisulfonate,bis(1-ethyl-1-methylpyrrolidinium) 1,4-butanedisulfonate,bis(1-butyl-1-methylpyrrolidinium) 1,4-butanedisulfonate,bis(1-methyl-1-propylpyrrolidinium) 1,4-butanedisulfonate,bis(1-ethylpyridinium) 1,4-butanedisulfonate,bis(1-ethyl-3-methylpyridinium) 1,4-butanedisulfonate,bis(1-butyl-3-methylpyridinium) 1,4-butanedisulfonate,bis(1-ethyl-4-methylpyridinium) 1,4-butanedisulfonate,bis(1-butylpyridinium) 1,4-butanedisulfonate,bis(1-butyl-4-methylpyridinium) 1,4-butanedisulfonate,bis(tetramethylphosphonium) 1,4-butanedisulfonate,bis(triethylmethylphosphonium) 1,4-butanedisulfonate,bis(tetraethylphosphonium) 1,4-butanedisulfonate, and the like.

Further, still other specific examples of the onium salt having adivalent linking group include bis(tetraethylammonium)4,4′-biphenyldisulfonate, bis(tetra-n-butylammonium)4,4′-biphenyldisulfonate, bis(methyltri-n-octylammonium)4,4′-biphenyldisulfonate, bis(amyltriethylammonium)4,4′-biphenyldisulfonate, bis(cyclohexyltrimethylammonium)4,4′-biphenyldisulfonate, bis(1-ethyl-3-methylimidazolium)4,4′-biphenyldisulfonate, bis(1-ethyl-2,3-dimethylimidazolium)4,4′-biphenyldisulfonate, bis(1-butyl-3-methylimidazolium)4,4′-biphenyldisulfonate, bis(1-butyl-2,3-dimethylimidazolium)4,4′-biphenyldisulfonate, bis(1-methyl-3-n-octylimidazolium)4,4′-biphenyldisulfonate, bis(1-hexyl-3-methylimidazolium)4,4′-biphenyldisulfonate, bis(2-ethyl-1,3-dimethylimidazolium)4,4′-biphenyldisulfonate, bis(1,3-dimethyl-2-n-propylimidazolium)4,4′-biphenyldisulfonate, bis(1,3-dimethyl-2-n-pentylimidazolium)4,4′-biphenyldisulfonate, bis(2-n-heptyl-1,3-dimethylimidazolium)4,4′-biphenyldisulfonate, bis(1-ethyl-1-methylpiperidinium)4,4′-biphenyldisulfonate, bis(1-butyl-1-methylpiperidinium)4,4′-biphenyldisulfonate, bis(1-ethyl-1-methylpyrrolidinium)4,4′-biphenyldisulfonate, bis(1-butyl-1-methylpyrrolidinium)4,4′-biphenyldisulfonate, bis(1-methyl-1-propylpyrrolidinium)4,4′-biphenyldisulfonate, bis(1-ethylpyridinium)4,4′-biphenyldisulfonate, bis(1-ethyl-3-methylpyridinium)4,4′-biphenyldisulfonate, bis(1-butyl-3-methylpyridinium)4,4′-biphenyldisulfonate, bis(1-ethyl-4-methylpyridinium)4,4′-biphenyldisulfonate, bis(1-butylpyridinium)4,4′-biphenyldisulfonate, bis(1-butyl-4-methylpyridinium)4,4′-biphenyldisulfonate, bis(tetramethylphosphonium)4,4′-biphenyldisulfonate, bis(triethylmethylphosphonium)4,4′-biphenyldisulfonate, bis(tetraethylphosphonium)4,4′-biphenyldisulfonate, and the like.

Further, still other specific examples of the onium salt having adivalent linking group include bis(tetraethylammonium)1,4-benzenedisulfonate, bis(tetra-n-butylammonium)1,4-benzenedisulfonate, bis(methyltri-n-octylammonium)1,4-benzenedisulfonate, bis(amyltriethylammonium)1,4-benzenedisulfonate, bis(cyclohexyltrimethylammonium)1,4-benzenedisulfonate, bis(1-ethyl-3-methylimidazolium)1,4-benzenedisulfonate, bis(1-ethyl-2,3-dimethylimidazolium)1,4-benzenedisulfonate, bis(1-butyl-3-methylimidazolium)1,4-benzenedisulfonate, bis(1-butyl-2,3-dimethylimidazolium)1,4-benzenedisulfonate, bis(1-methyl-3-n-octylimidazolium)1,4-benzenedisulfonate, bis(1-hexyl-3-methylimidazolium)1,4-benzenedisulfonate, bis(2-ethyl-1,3-dimethylimidazolium)1,4-benzenedisulfonate, bis(1,3-dimethyl-2-n-propylimidazolium)1,4-benzenedisulfonate, bis(1,3-dimethyl-2-n-pentylimidazolium)1,4-benzenedisulfonate, bis(2-n-heptyl-1,3-dimethylimidazolium)1,4-benzenedisulfonate, bis(1-ethyl-1-methylpiperidinium)1,4-benzenedisulfonate, bis(1-butyl-1-methylpiperidinium)1,4-benzenedisulfonate, bis(1-ethyl-1-methylpyrrolidinium)1,4-benzenedisulfonate, bis(1-butyl-1-methylpyrrolidinium)1,4-benzenedisulfonate, bis(1-methyl-1-propylpyrrolidinium)1,4-benzenedisulfonate, bis(1-ethylpyridinium) 1,4-benzenedisulfonate,bis(1-ethyl-3-methylpyridinium) 1,4-benzenedisulfonate,bis(1-butyl-3-methylpyridinium) 1,4-benzenedisulfonate,bis(1-ethyl-4-methylpyridinium) 1,4-benzenedisulfonate,bis(1-butylpyridinium) 1,4-benzenedisulfonate,bis(1-butyl-4-methylpyridinium) 1,4-benzenedisulfonate,bis(tetramethylphosphonium) 1,4-benzenedisulfonate,bis(triethylmethylphosphonium) 1,4-benzenedisulfonate,bis(tetraethylphosphonium) 1,4-benzenedisulfonate, and the like.

Further, still other specific examples of the onium salt having adivalent linking group include bis(tetraethylammonium)1,5-naphthalenedisulfonate, bis(tetra-n-butylammonium)1,5-naphthalenedisulfonate, bis(methyltri-n-octylammonium)1,5-naphthalenedisulfonate, bis(amyltriethylammonium)1,5-naphthalenedisulfonate, bis(cyclohexyltrimethylammonium)1,5-naphthalenedisulfonate, bis(1-ethyl-3-methylimidazolium)1,5-naphthalenedisulfonate, bis(1-ethyl-2,3-dimethylimidazolium)1,5-naphthalenedisulfonate, bis(1-butyl-3-methylimidazolium)1,5-naphthalenedisulfonate, bis(1-butyl-2,3-dimethylimidazolium)1,5-naphthalenedisulfonate, bis(1-methyl-3-n-octylimidazolium)1,5-naphthalenedisulfonate, bis(1-hexyl-3-methylimidazolium)1,5-naphthalenedisulfonate, bis(2-ethyl-1,3-dimethylimidazolium)1,5-naphthalenedisulfonate, bis(1,3-dimethyl-2-n-propylimidazolium)1,5-naphthalenedisulfonate, bis(1,3-dimethyl-2-n-pentylimidazolium)1,5-naphthalenedisulfonate, bis(2-n-heptyl-1,3-dimethylimidazolium)1,5-naphthalenedisulfonate, bis(1-ethyl-1-methylpiperidinium)1,5-naphthalenedisulfonate, bis(1-butyl-1-methylpiperidinium)1,5-naphthalenedisulfonate, bis(1-ethyl-1-methylpyrrolidinium)1,5-naphthalenedisulfonate, bis(1-butyl-1-methylpyrrolidinium)1,5-naphthalenedisulfonate, bis(1-methyl-1-propylpyrrolidinium)1,5-naphthalenedisulfonate, bis(1-ethylpyridinium)1,5-naphthalenedisulfonate, bis(1-ethyl-3-methylpyridinium)1,5-naphthalenedisulfonate, bis(1-butyl-3-methylpyridinium)1,5-naphthalenedisulfonate, bis(1-ethyl-4-methylpyridinium)1,5-naphthalenedisulfonate, bis(1-butylpyridinium)1,5-naphthalenedisulfonate, bis(1-butyl-4-methylpyridinium)1,5-naphthalenedisulfonate, bis(tetramethylphosphonium)1,5-naphthalenedisulfonate, bis(triethylmethylphosphonium)1,5-naphthalenedisulfonate, bis(tetraethylphosphonium)1,5-naphthalenedisulfonate, and the like.

Further, still other specific examples of the onium salt having adivalent linking group include bis(tetraethylammonium)diphenylether-4,4′-disulfonate, bis(tetra-n-butylammonium)diphenylether-4,4′-disulfonate, bis(methyltri-n-octylammonium)diphenylether-4,4′-disulfonate, bis(amyltriethylammonium)diphenylether-4,4′-disulfonate, bis(cyclohexyltrimethylammonium)diphenylether-4,4′-disulfonate, bis(1-ethyl-3-methylimidazolium)diphenylether-4,4′-disulfonate, bis(1-ethyl-2,3-dimethylimidazolium)diphenylether-4,4′-disulfonate, bis(1-butyl-3-methylimidazolium)diphenylether-4,4′-disulfonate, bis(1-butyl-2,3-dimethylimidazolium)diphenylether-4,4′-disulfonate, bis(1-methyl-3-n-octylimidazolium)diphenylether-4,4′-disulfonate, bis(1-hexyl-3-methylimidazolium)diphenylether-4,4′-disulfonate, bis(2-ethyl-1,3-dimethylimidazolium)diphenylether-4,4′-disulfonate, bis(1,3-dimethyl-2-n-propylimidazolium)diphenylether-4,4′-disulfonate, bis(1,3-dimethyl-2-n-pentylimidazolium)diphenylether-4,4′-disulfonate, bis(2-n-heptyl-1,3-dimethylimidazolium)diphenylether-4,4′-disulfonate, bis(1-ethyl-1-methylpiperidinium)diphenylether-4,4′-disulfonate, bis(1-butyl-1-methylpiperidinium)diphenylether-4,4′-disulfonate, bis(1-ethyl-1-methylpyrrolidinium)diphenylether-4,4′-disulfonate, bis(1-butyl-1-methylpyrrolidinium)diphenylether-4,4′-disulfonate, bis(1-methyl-1-propylpyrrolidinium)diphenylether-4,4′-disulfonate, bis(1-ethylpyridinium)diphenylether-4,4′-disulfonate, bis(1-ethyl-3-methylpyridinium)diphenylether-4,4′-disulfonate, bis(1-butyl-3-methylpyridinium)diphenylether-4,4′-disulfonate, bis(1-ethyl-4-methylpyridinium)diphenylether-4,4′-disulfonate, bis(1-butylpyridinium)diphenylether-4,4′-disulfonate, bis(1-butyl-4-methylpyridinium)diphenylether-4,4′-disulfonate, bis(tetramethylphosphonium)diphenylether-4,4′-disulfonate, bis(triethylmethylphosphonium)diphenylether-4,4′-disulfonate, bis(tetraethylphosphonium)diphenylether-4,4′-disulfonate, and the like.

Further, still other specific examples of the onium salt having adivalent linking group include bis(tetraethylammonium)1,4-butanedioldisulfonate, bis(tetra-n-butylammonium)1,4-butanedioldisulfonate, bis(methyltri-n-octylammonium)1,4-butanedioldisulfonate, bis(amyltriethylammonium)1,4-butanedioldisulfonate, bis(cyclohexyltrimethylammonium)1,4-butanedioldisulfonate, bis(1-ethyl-3-methylimidazolium)1,4-butanedioldisulfonate, bis(1-ethyl-2,3-dimethylimidazolium)1,4-butanedioldisulfonate, bis(1-butyl-3-methylimidazolium)1,4-butanedioldisulfonate, bis(1-butyl-2,3-dimethylimidazolium)1,4-butanedioldisulfonate, bis(1-methyl-3-n-octylimidazolium)1,4-butanedioldisulfonate, bis(1-hexyl-3-methylimidazolium)1,4-butanedioldisulfonate, bis(2-ethyl-1,3-dimethylimidazolium)1,4-butanedioldisulfonate, bis(1,3-dimethyl-2-n-propylimidazolium)1,4-butanedioldisulfonate, bis(1,3-dimethyl-2-n-pentylimidazolium)1,4-butanedioldisulfonate, bis(2-n-heptyl-1,3-dimethylimidazolium)1,4-butanedioldisulfonate, bis(1-ethyl-1-methylpiperidinium)1,4-butanedioldisulfonate, bis(1-butyl-1-methylpiperidinium)1,4-butanedioldisulfonate, bis(1-ethyl-1-methylpyrrolidinium)1,4-butanedioldisulfonate, bis(1-butyl-1-methylpyrrolidinium)1,4-butanedioldisulfonate, bis(1-methyl-1-propylpyrrolidinium)1,4-butanedioldisulfonate, bis(1-ethylpyridinium)1,4-butanedioldisulfonate, bis(1-ethyl-3-methylpyridinium)1,4-butanedioldisulfonate, bis(1-butyl-3-methylpyridinium)1,4-butanedioldisulfonate, bis(1-ethyl-4-methylpyridinium)1,4-butanedioldisulfonate, bis(1-butylpyridinium)1,4-butanedioldisulfonate, bis(1-butyl-4-methylpyridinium)1,4-butanedioldisulfonate, bis(tetramethylphosphonium)1,4-butanedioldisulfonate, bis(triethylmethylphosphonium)1,4-butanedioldisulfonate, bis(tetraethylphosphonium)1,4-butanedioldisulfonate, and combinations of an anion represented bythe following formula (5) and various cations.

Further, specific examples of the onium salt having a trivalent linkinggroup include tris(tetraethylammonium) naphthalene-1,3,6-trisulfonate,tris(tetra-n-butylammonium) naphthalene-1,3,6-trisulfonate,tris(methyltri-n-octylammonium) naphthalene-1,3,6-trisulfonate,tris(amyltriethylammonium) naphthalene-1,3,6-trisulfonate,tris(cyclohexyltrimethylammonium) naphthalene-1,3,6-trisulfonate,tris(1-ethyl-3-methylimidazolium) naphthalene-1,3,6-trisulfonate,tris(1-ethyl-2,3-dimethylimidazolium) naphthalene-1,3,6-trisulfonate,tris(1-butyl-3-methylimidazolium) naphthalene-1,3,6-trisulfonate,tris(1-butyl-2,3-dimethylimidazolium) naphthalene-1,3,6-trisulfonate,tris(1-methyl-3-n-octylimidazolium) naphthalene-1,3,6-trisulfonate,tris(1-hexyl-3-methylimidazolium) naphthalene-1,3,6-trisulfonate,tris(2-ethyl-1,3-dimethylimidazolium) naphthalene-1,3,6-trisulfonate,tris(1,3-dimethyl-2-n-propylimidazolium) naphthalene-1,3,6-trisulfonate,tris(1,3-dimethyl-2-n-pentylimidazolium) naphthalene-1,3,6-trisulfonate,tris(2-n-heptyl-1,3-dimethylimidazolium) naphthalene-1,3,6-trisulfonate,tris(1-ethyl-1-methylpiperidinium) naphthalene-1,3,6-trisulfonate,tris(1-butyl-1-methylpiperidinium) naphthalene-1,3,6-trisulfonate,tris(1-ethyl-1-methylpyrrolidinium) naphthalene-1,3,6-trisulfonate,tris(1-butyl-1-methylpyrrolidinium) naphthalene-1,3,6-trisulfonate,tris(1-methyl-1-propylpyrrolidinium) naphthalene-1,3,6-trisulfonate,tris(1-ethylpyridinium) naphthalene-1,3,6-trisulfonate,tris(1-ethyl-3-methylpyridinium) naphthalene-1,3,6-trisulfonate,tris(1-butyl-3-methylpyridinium) naphthalene-1,3,6-trisulfonate,tris(1-ethyl-4-methylpyridinium) naphthalene-1,3,6-trisulfonate,tris(1-butylpyridinium) naphthalene-1,3,6-trisulfonate,tris(1-butyl-4-methylpyridinium) naphthalene-1,3,6-trisulfonate,tris(tetramethylphosphonium) naphthalene-1,3,6-trisulfonate,tris(triethylmethylphosphonium) naphthalene-1,3,6-trisulfonate,tris(tetraethylphosphonium) naphthalene-1,3,6-trisulfonate, and thelike.

Further, specific examples of the onium salt having a tetravalentlinking group include tetrakis(tetraethylammonium)1,3,6,8-pyrenetetrasulfonate, tetrakis(tetra-n-butylammonium)1,3,6,8-pyrenetetrasulfonate, tetrakis(methyltri-n-octylammonium)1,3,6,8-pyrenetetrasulfonate, tetrakis(amyltriethylammonium)1,3,6,8-pyrenetetrasulfonate, tetrakis(cyclohexyltrimethylammonium)1,3,6,8-pyrenetetratrisulfonate, tetrakis(1-ethyl-3-methylimidazolium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-ethyl-2,3-dimethylimidazolium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-butyl-3-methylimidazolium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-butyl-2,3-dimethylimidazolium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-methyl-3-n-octylimidazolium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-hexyl-3-methylimidazolium)1,3,6,8-pyrenetetrasulfonate, tetrakis(2-ethyl-1,3-dimethylimidazolium)1,3,6,8-pyrenetetrasulfonate,tetrakis(1,3-dimethyl-2-n-propylimidazolium)1,3,6,8-pyrenetetrasulfonate,tetrakis(1,3-dimethyl-2-n-pentylimidazolium)1,3,6,8-pyrenetetrasulfonate,tetrakis(2-n-heptyl-1,3-dimethylimidazolium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-ethyl-1-methylpiperidinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-butyl-1-methylpiperidinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-ethyl-1-methylpyrrolidinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-butyl-1-methylpyrrolidinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-methyl-1-propylpyrrolidinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-ethylpyridinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-ethyl-3-methylpyridinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-butyl-3-methylpyridinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-ethyl-4-methylpyridinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-butylpyridinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(1-butyl-4-methylpyridinium)1,3,6,8-pyrenetetrasulfonate, tetrakis(tetramethylphosphonium)1,3,6,8-pyrenetetrasulfonate, tetrakis(triethylmethylphosphonium)1,3,6,8-pyrenetetrasulfonate, tetrakis(tetraethylphosphonium)1,3,6,8-pyrenetetrasulfonate, and the like. These onium salts may beused alone or in combination of two of more.

The onium salt according to the present invention can be obtained bymethods known in the art. For instance, they can be prepared from thecorresponding onium halides as described in, Hiroyuki Ohno et al., J.Am. Chem. Soc., 2005, 27, 2398-2399; or in Peter Wasserscheid et al.,Green Chemistry, 2002, 4, 134-138.

The content of the aforementioned onium salt (b) in the adhesivecomposition is, preferably from 10 to 20000 ppm, more preferably from 25to 15000 ppm, and further preferably from 50 to 10000 ppm, per 100 partsby mass of 2-cyanoacrylic acid ester (a). When the content is within theabove range, the effect of hardening acceleration is sufficientlyexhibited, and the storage stability of the adhesive composition is keptgood.

The reason why the aforementioned onium salt improves the adhesion rateon non-polar hard-to-bond materials and bond gap curability withoutimpairing the storage stability of the adhesive composition is not yetclear, however, can be presumed as follows. Since the conjugate acid ofthe weakly nucleophilic anion that constitutes the onium salt is astrong acid, it releases an anion which is nucleophilic and thus servesas a polymerization initiator of the 2-cyanoacrylic acid ester when itreacts with a salt that is present on a surface of an adherend or in anair adjacent to the adhesive. On the other hand, since such a salt isnot present during storage, the aforementioned anion exchange reactiondoes not take place to initiate the release of the highly reactiveanion, so that excellent storage stability is maintained. Since theonium salt according to the present invention has a multifunctionalstructure in which two or more anions are linked together by way of alinking group, the linking group adheres or oriented to a non-polaradherend or an adjacent air to perform coupling function. As a result,the anion site tends to locate the interface or surface of adhesion, andthus becomes easier to cause the reaction with the salt.

The adhesive composition of the present invention may contain, inaddition to the aforementioned onium salts, another hardeningaccelerator conventionally blended in these types of adhesivecompositions. Examples of such hardening accelerators includepolyalkylene oxides, crown ethers, silacrown ethers, calixarenes,cyclodextrins, and pyrogallol-based cyclic compounds.

The polyalkylene oxides refer to polyalkylene oxides and the derivativesthereof, and examples thereof include those disclosed in Japanese PatentPublication (Kokoku) No. Sho. 60-37836, Japanese Patent Publication(Kokoku) No. Hei. 1-43790, Japanese Patent Publication (Laid-open) No.Sho. 63-128088, Japanese Patent Publication (Laid-open) No. Hei.3-167279, U.S. Pat. No. 4,386,193, and U.S. Pat. No. 4,424,327. Concreteexamples thereof include (1) polyalkylene oxides such as diethyleneglycol, triethylene glycol, polyethylene glycol, and polypropyleneglycol; and (2) derivatives of polyalkylene oxides such as polyethyleneglycol monoalkyl esters, polyethylene glycol dialkyl esters,polypropylene glycol dialkyl esters, diethylene glycol monoalkyl ethers,diethylene glycol dialkyl ethers, dipropylene glycol monoalkyl ethers,and dipropylene glycol dialkyl ethers.

Examples of the crown ethers include those disclosed in, for instance,Japanese Patent Publication (Kokoku) No. Sho. 55-2238 and JapanesePatent Publication (Laid-Open) No. Hei. 3-167279. Concrete examplesthereof include 12-crown-4, 15-crown-5, 18-crown-6, benzo-12-crown-4,benzo-15-crown-5, benzo-18-crown-6, dibenzo-18-crown-6,dibenzo-24-crown-8, dibenzo-30-crown-10, tribenzo-18-crown-6,asym-dibenzo-22-crown-6, dibenzo-14-crown-4, dicyclohexyl-24-crown-8,cyclohexyl-12-crown-4, 1,2-decalyl-15-crown-5, 1,2-naphtho-15-crown-5,3,4,5-naphthyl-16-crown-5, 1,2-methylbenzo-18-crown-6,1,2-tert-butyl-18-crown-6, and 1,2-vinylbenzo-15-crown-5. Examples ofthe silacrown ethers include, for example, those disclosed in JapanesePatent Publication (Laid-Open) No. Sho. 60-168775. Concrete examplesthereof include dimethylsila-11-crown-4, dimethylsila-14-crown-5, anddimethylsila-17-crown-6.

Examples of the calixarenes include those disclosed in Japanese PatentPublication (Laid-Open) No. Sho. 60-179482, Japanese Patent Publication(Laid-Open) No. Sho. 62-235379, and Japanese Patent Publication(Laid-Open) No. Sho. 63-88152. Concrete examples thereof include5,11,17,23,29,35-hexa-tert-butyl-37,38,39,40,41,42-hexahydroxycalix[6]arene,37,38,39,40,41,42-hexahydroxycalix[6]arene,37,38,39,40,41,42-hexa-(2-oxo-2-ethoxy)-ethoxycalix[6]arene,25,26,27,28-tetra-(2-oxo-2-ethoxy)-ethoxycalix[4]arene, and tetraethyl4-tert-butylcalix[4]arene-O,O′,O″,O′″-tetraacetate. Examples of thecyclodextrins include those disclosed in Japanese Patent Publication(Kohyo) No. Hei. 5-505835. Concrete examples thereof include α-, β-, orγ-cyclodextrins. Examples of the pyrogallol-based cyclic compoundsinclude compounds disclosed in Japanese Patent Publication (Laid-Open)No. 2000-191600. Concrete examples thereof include3,4,5,10,11,12,17,18,19,24,25,26-dodecaethoxycarbomethoxy-C-1,C-8,C-15,C-22-tetramethyl[14]-metacyclophane.These hardening accelerators may be used either alone or in combinationof two or more thereof.

In the adhesive composition, the content of the hardening acceleratorsother than the onium salt is preferably from 10 to 30000 ppm, morepreferably from 50 to 20000 ppm, and most preferably from 100 to 10000ppm relative to 100 parts by mass of 2-cyanoacrylic acid ester. Theadhesive composition can be improved in the adhesion rate on variousadherends without impairing the storage stability so long as the contentfalls within the range of from 10 to 30000 ppm.

In addition to the above hardening accelerator, the adhesive compositionof the present invention may contain stabilizers, plasticizers,thickeners, particles, colorants, fragrances, solvents, strengthimprovers or others that have conventionally been employed in adhesivecompositions containing 2-cyanoacrylic acid ester, depending on theobjectives, in proper amounts that do not impair curability, adhesionstrength or the like of the adhesive composition.

The stabilizers include (1) anion polymerization inhibitors, such assulfur dioxide, aliphatic sulfonates such as methanesulfonate, aromaticsulfonates such as p-toluenesulfonate, boron trifluoride complexes suchas boron trifluoride methanol and boron trifluoride diethyl ether, HBF₄,and trialkyl borate; and (2) radical polymerization inhibitors such ashydroquinone, hydroquinone monomethyl ether, t-butylcatechol, catechol,and pyrogallol. These stabilizers may be used alone, or in a combinationof two or more thereof.

The plasticizers include triethyl acetyl citrate, tributyl acetylcitrate, dimethyl adipate, diethyl adipate, dimethyl sebacate, dimethylphthalate, diethyl phthalate, dibutyl phthalate, diisodecyl phthalate,dihexyl phthalate, diheptyl phthalate, dioctyl phthalate,bis(2-ethylhexyl) phthalate, diisononyl phthalate, diisotridecylphthalate, dipentadecyl phthalate, dioctyl terephthalate, diisononylisophthalate, decyl toluate, bis(2-ethylhexyl) camphorate,2-ethylhexylcyclohexyl carboxylate, diisobutyl fumarate, diisobutylmaleate, caproic triglyceride, 2-ethylhexyl benzoate, and dipropyleneglycol dibenzoate. Among them, preferred from the viewpoint of goodmiscibility with 2-cyanoacrylic acid ester and of high plasticizingefficiency are tributyl acetyl citrate, dimethyl adipate, dimethylphthalate, 2-ethylhexyl benzoate, and dipropylene glycol dibenzoate.These plasticizers may be used alone or in combination of two or morethereof.

The thickeners include polymethylmethacrylates, copolymers ofmethylmethacrylate and an acrylate, copolymers of methylmethacrylate andanother methacrylate, acrylic rubbers, polyvinylchloride, polystyrene,cellulose esters, polyalkyl-2-cyanoacrylate, and ethylene-vinyl acetatecopolymers. These thickeners may be used either alone or in combinationof two or more thereof.

EXAMPLES

The present invention is explained in further detail by way of Examplesbelow. However, the present invention is not limited to these Examples,but various modifications and changes can be made to the presentinvention without departing from the gist of the present invention. Inthe description below, parts and percentages are based on mass unlessotherwise mentioned.

1. Evaluation Method (1) Adhesion Rate

-   -   Natural rubber: A natural rubber tube having an inner diameter        of 6 mm and an outer diameter of 10 mm was cut by a cutter, and        then the cutting surfaces were bonded together with the adhesive        composition according to the present invention and stood still        for a predetermined time to fix. A period until the tensile        adhesion strength reached over 0.16 N/mm² was taken as adhesion        time.    -   Bond gap curability: Two square columns were provided as test        pieces which were made of polyvinyl chloride resin (12.7 mm        (vertical)×12.7 mm (transverse)×38 mm (length)). A polyethylene        mesh (NIP (polyethylene) strong net (trade name) manufactured by        NBC Meshtec Inc.; product number 200; 30 mm (length)×30 mm        (width)×100 μm (thickness)) was sandwiched between the end        surfaces (12.7 mm (vertical)×12.7 mm (transverse)) of the two        square columns to bond them together and stood still for a        predetermined time to fix. A period until the tensile adhesion        strength reached over 0.16 N/mm² was taken as adhesion time.

(2) Viscosity

Viscosity was measured using E-type viscometer at 25° C. and 100 rpm.

(3) Storage Stability

Evaluation was made by comparing the viscosity measured at the initialstage with the viscosity measured after storage for one week under theenvironment of 50° C. and 95% RH. For the storage, 1.5 g of the adhesivecomposition was sealed in a 2 g polyethylene container.

2. Synthesis of Onium Salt Synthesis Example 1

In a 50-ml eggplant shape flask were charged 1.466 g (10.00 mmol) of1-ethyl-3-methylimidazolium chloride (see Table 1), 13.2 g (20 mgchemical equivalent) of anion exchange resin (AMBERLITE IRA900A OH AG(trade name), strong base type, manufactured by Organo Corporation), and25 ml of ion-exchange water, and were stirred for 48 hours under roomtemperature. After filtering off the ion exchange resin, 5 ml solutionin ion-exchanged water of 1.572 g (5.00 mmol) of 4,4′-biphenyldisulfonicacid (see Table 1) was slowly dropped into the resulting product underice cooling. Then, the ice bath was removed, and additional stirring wascontinued for 12 hours under room temperature. Then, the reactionsolution was rinsed with 25 ml of toluene, purified with ion exchangeresin, and then condensed under reduced pressure. The thus-obtainedresidue was dissolved in 25 ml of methanol to filter off the insolublematter. The solvent was distilled away under reduced pressure to obtain2.540 g of onium salt A (bis(1-ethyl-3-methylimidazolium)4.4′-biphenyldisulfonate) (see Table 1) as pale yellow solid.

Synthesis Example 2

In a 50-ml eggplant shape flask were charged 4.042 g (10.00 mmol) ofmethyltri-n-octylammonium chloride (see Table 1), 13.2 g (20 mg chemicalequivalent) of anion exchange resin (AMBERLITE IRA900A OH AG (tradename), strong base type, manufactured by Organo Corporation), and 20 mlof toluene, and were stirred for 48 hours under room temperature. Afterfiltering off the ion exchange resin, 5 ml solution in ion-exchangedwater of 1.572 g (5.00 mmol) of 4,4′-biphenyldisulfonic acid (seeTable 1) was slowly dropped into the resulting product under icecooling. Then, the ice bath was removed, and additional stirring wascontinued for 12 hours under room temperature. Then, the reactionsolution was rinsed with 10 ml of ion exchanged water three times, andthen condensed under reduced pressure. The thus-obtained residue wasdissolved in 25 ml of methanol to filter off the insoluble matter. Thesolvent was distilled away under reduced pressure to obtain 4.847 g ofonium salt B (bis(methyltri-n-octylammonium) 4.4′-biphenyldisulfonate)(see Table 1) as pale yellow semi-solid.

Synthesis Examples 3-5 and 7

Onium salts were synthesized in accordance with Synthetic Example 1,except that various quaternary nitrogen containing halides and sulfonicacids shown in Table 1 were used as raw materials in the chargingamounts shown in Table 1.

Synthesis Examples 6, 8 and 9

Onium salts were synthesized in accordance with Synthetic Example 2,except that various quaternary nitrogen containing halides and sulfonicacids shown in Table 1 were used as raw materials in the charged amountsshown in Table 1.

TABLE 1 Onium Salt Compounds used for synthesis of onium salts SynthesisYield Charged Charged Example Type (g) Quaternary nitrogen containinghalides Amount (g) Sulfonic acid Amount (g) 1 A 2.5401-ethyl-3-methylimidazolium chloride 1.466 4,4′-biphenyldisulfonic acid1.572 2 B 4.847 methyltri-n-octylammonium chloride 4.0424,4′-biphenyldisulfonic acid 1.572 3 C 2.692 1-butyl-3-methylpyridiniumbromide 2.301 4,4′-biphenyldisulfonic acid 1.572 4 D 2.6171-butyl-1-methylpyrrolidinium chloride 1.777 4,4′-biphenyldisulfonicacid 1.572 5 E 2.143 1-ethyl-3-methylimidazolium chloride 1.4661,2-ethanedisulfonic acid dihydrate 1.131 6 F 4.568methyltri-n-octylammonium chloride 4.042 1,2-ethanedisulfonic aciddihydrate 1.131 7 G 2.262 1-ethyl-3-methylimidazolium chloride 1.6061,4-butanedisulfonic acid 1.091 8 H 4.578 methyltri-n-octylammoniumchloride 4.042 1,4-butanedisulfonic acid 1.091 9 I 4.314methyltri-n-octylammonium chloride 4.042 methanesulfonic acid 0.961

3. Preparation of 2-Cyanoacrylate-Based Adhesive Composition Examples1-10 and Comparative Example 1-5

To ethyl 2-cyanoacrylate were added 40 ppm of sulfur dioxide and 1000ppm of hydroquinone (with respect to 100 parts by mass of ethyl2-cyanocrylate), and various onium salts or additives were blendedtherewith to obtain adhesive compositions which were then subjected tovarious tests. The results are given in Tables 2 and 3.

TABLE 2 Adhesion rate Onium salt (seconds) Viscosity (mPa · s) ContentNatural Bond After 1 week Type (ppm) rubber gap Initial (50° C., 95% RH)Example 1 bis(1-ethyl-3-methylimidazolium) A 100 20 90 2.2 2.44,4′-biphenyldisulfonate 2 bis(1-ethyl-3-methylimidazolium) A 500 10 452.5 2.7 4,4′-biphenyldisulfonate 3 bis(methyltri-n-octylammonium) B 10020 60 2.4 2.6 4,4′-biphenyldisulfonate 4 bis(methyltri-n-octylammonium)B 200 10 60 2.4 2.7 4,4′-biphenyldisulfonate 5bis(1-butyl-3-methylpyridinium) C 10000 5 30 3.9 4.94,4′-biphenyldisulfonate 6 bis(1-butyl-1-methylpyrrolidinium) D 150 2060 2.5 2.8 4,4′-biphenyldisulfonate 7 bis(1-ethyl-3-methylimidazolium) E75 15 45 2.5 2.7 1,2-ethanedisulfonate 8 bis(methyltri-n-octylammonium)F 100 10 30 2.6 2.8 1,2-ethanedisulfonate 9bis(1-ethyl-3-methylimidazolium) G 200 15 60 2.4 2.81,4-butanedisulfonate 10 bis(methyltri-n-octylammonium) H 100 20 90 2.32.5 1,4-butanedisulfonate

TABLE 3 Adhesion rate Additive (seconds) Viscosity (mPa · s) ContentNatural Bond After 1 week Type Trade name (ppm) Rubber gap Initial (50°C., 95% RH) Comparative 1 15-Crown-5 Crown Ether O-15, 2500 30 120 2.12.3 Example manufactured by NIPPON SODA CO., LTD. 2 Tetraethyl CALIXB4-EA, manufactured 2000 30 120 2.2 2.4 4-tert-Butylcalix[4]arene- bySugai Chemical IND. O,O′,O″,O″′-tetraacetate CO., LTD. 31-ethyl-3-methylimidazolium Reagent, Tokyo Chemical 200 30 300 2.5 2.8methanesulfonate Industry Co., Ltd. 4 Methyltri-n-octylammonium Oniumsalt I 150 30 300 2.5 2.9 methanesulfonate 5 Additive-free — — 90 3002.1 2.1

The results in Tables 2 and 3 show that the adhesive compositions inExamples 1-10 exhibit excellent adhesion rates on natural rubber andgood bond gap curability, compared with the adhesive compositionscontaining conventional hardening accelerators (Comparative Examples 1and 2) and the adhesive compositions containing onium salts fallingoutside the present invention (Comparative Examples 3 and 4), and alsoshow a viscosity change of 1.3 or less even after one week at 50° C. and95% RH, and thus are excellent in storage stability.

INDUSTRIAL APPLICABILITY

The present invention which is based on 2-cyanoacrylic acid ester can beutilized as a so-called instantaneous adhesive in a wide range ofproducts and technical fields in various types of industrial fieldsincluding household and medical fields, and is particularly useful foradhesion of hard-to-bond materials and adhesion in the case, forexample, where convex or concavo exits on surfaces of adherends or thecase where there is a gap between adherends.

1. A 2-cyanoacrylate-based adhesive composition which comprises (a) a 2-cyanoacrylic acid ester and (b) an onium salt represented by the following formula (1): nC⁺A⁻ _(n)-X  (1) wherein, in formula (1), C⁺ represents an onium cation, A⁻ represents at least one anion selected from the group consisting of —SO₃ ⁻, —OSO₃ ⁻ and an imide anion represented by the following formula (2), X represents a linking group which connects at least two anions together, and n is an integer of 2 or more,

wherein, in formula (2), R¹ represents a fluorine atom, alkyl group, cycloalkyl group, perfluoroalkyl group, aryl group, aralkyl group, alkenyl group or alkynyl group.
 2. The 2-cyanoacrylate-based adhesive composition according to claim 1, wherein the cation of the onium salt (b) is at least one onium cation selected from a group consisting of a quaternary ammonium cation, a quaternary phosphonium cation, an imidazolium cation, a pyridinium cation, and a tertiary sulfonium cation.
 3. The 2-cyanoacrylate-based adhesive composition according to claim 1, wherein the anion of the onium salt (b) is at least one anion selected from a group consisting of —SO₃ ⁻, —OSO₃ ⁻, a fluorosulfonylimide anion and a perfluoroalkylsulfonylimide anion.
 4. The 2-cyanoacrylate-based adhesive composition according to claim 1, wherein the linking group X in the formula (1) is a divalent linking group.
 5. The 2-cyanoacrylate-based adhesive composition according to claim 4, wherein the linking group X in formula (1) is at least one divalent linking group selected from the group consisting of an alkylene group, a cycloalkylene group, an arylene group and a biphenyl group.
 6. The 2-cyanoacrylate-based adhesive composition according to claim 1, wherein the content of the onium salt (b) is 10 to 20,000 ppm relative to 100 parts by mass of the 2-cyanoacrylic acid ester (a).
 7. A 2-cyanoacrylate-based adhesive composition which comprises (a) a 2-cyanoacrylic acid ester; and (b) an onium salt represented by the following formula (1): nC⁺A⁻ _(n)-X  (1) wherein C⁺ represents an onium cation comprising at least one onium cation selected from a group consisting of a quaternary ammonium cation, a quaternary phosphonium cation, an imidazolium cation, a pyridinium cation, and a tertiary sulfonium cation, A⁻ represents at least one anion selected from the group consisting of —SO₃ ⁻, —OSO₃ ⁻ and an imide anion, X represents a divalent linking group which connects at least two anions together, n is an integer of 2 or more, and said imide anion is represented by the following formula (2)

wherein R¹ represents a fluorine atom, alkyl group, cycloalkyl group, perfluoroalkyl group, aryl group, aralkyl group, alkenyl group or alkynyl group.
 8. The 2-cyanoacrylate-based adhesive composition according to claim 7, wherein the anion of the onium salt (b) is at least one anion selected from a group consisting of —SO₃ ⁻, —OSO₃ ⁻, a fluorosulfonylimide anion and a perfluoroalkylsulfonylimide anion.
 9. The 2-cyanoacrylate-based adhesive composition according to claim 8, wherein the divalent linking group X in general formula (1) comprises a divalent linking group selected from the group consisting of an alkylene group, a cycloalkylene group, an arylene group and a biphenyl group.
 10. The 2-cyanoacrylate-based adhesive composition according to claim 7, wherein the content of the onium salt (b) is 10 to 20,000 ppm relative to 100 parts by mass of the 2-cyanoacrylic acid ester (a). 